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A statement on the Zoo's website said: "We are delighted to say that today would appear to be the day for panda mating. During this time the panda cam will be unavailable."

Keepers were planning to put them together several times over the two-day period, for 15 minutes at a time.

They did not fight during their first meeting, which was a good sign, and if they fail take things further on their own, keepers may intervene by pushing them together with a bamboo pole and lift Sweetie’s tail.

Both have had cubs before, although not with each other, and according to the zoo they are "pandas of the world".

Sunshine has been eating twice his normal intake of bamboo for the past two weeks in an apparent bid to "build up his strength", while Sweetie has been cutting down - both said to be positive developments.

Panda pregnancies can last for 85 to 100 days, but if the pair do mate it will be mid-July before the result is known.

In January giant panda Yang Guang has been taken outof public display after coming down with colic

Visitor numbers have increased by 200 per cent since the pandas arrived from China in December - in a £600,000-a-year deal for ten years - and panda cubs would be a huge boost to the visitor attraction.

If all else fails, Sweetie could be artificially inseminated, but it is unlikely that would be done this year.